This invention relates to iron-nickel alloy materials for use in forming electronic parts such as shadow masks and lead frames with fine etching. More particularly, this invention relates to Fe--Ni alloy materials to be used for electronic parts, with their perforation etchability enhanced through the control of the nitrogen content in the Fe--Ni alloy material.
In recent years, there has been a steady increase in the degree of integration in the field of microprocessors and other integrated circuit parts. Among lead frames, for instance, multi-pin type parts having 200 or more pins are coming into predominant use. Those multi-pin type parts are made chiefly of a Fe--Ni alloy known as "42 Alloy (Fe-42% Ni alloy)" because of its strength.
In the manufacture of shadow masks for color picture tubes too, another Fe--Ni alloy called "36 Alloy (Fe-36% Ni alloy)" whose low coefficient of thermal expansion is favorable for color purity is in use.
In general, multi-pin lead frames and high-precision shadow masks for which dimensional accuracy is a prime consideration are made using photoetching. For finer pitches of grooves, a more finely etchable material, especially a material having a greater ratio of the etching rate in the thickness direction to the etching rate in the side direction, known as the "etch factor" is required. Fe--Ni alloys have low etch factors compared to copper alloys and aluminum-killed steels. This has been an obstacle in the way toward finer-pitching of Fe--Ni alloys.
For the purposes of the invention, the etch factor (EF) is expressed, in FIG. 1 that schematically depicts an etched state, as
EF=d/SE
where d is the depth of etching and SE is the side etched amount.
The side etched amount (SE) means the amount etched to excess beyond the edge of an opening made in a resist layer and is expressed as SE=(R-r)/2 where R is the diameter of the opening actually formed by etching and r is the diameter of the exposed area or opening in the resist layer.
Some proposals have hitherto been made to improve the etchability of Fe--Ni alloys by decreasing the proportions of nonmetallic inclusions and trace impurities in the alloys. However, none of the proposed methods have been fully satisfactory in improving their etching properties.
Meanwhile, another approach has been proposed which comprises intensively working a Fe--Ni alloy material to increase the texture concentration of the {100} planes in the worked area and thereby improve the etchability. This method again has drawbacks in that it can cause roughening or streaking of the etched surface and, moreover, increases the anisotropy of the etch factor.
The present invention aims at providing Fe--Ni alloy materials that lend themselves excellently to fabrication as by etching and permit the manufacture of such electronic parts as multi-pin lead frames and high-precision shadow masks by photoetching with good precision, without the drawbacks of the prior art.